Microelectronic contact structure

ABSTRACT

Spring contact elements are fabricated by depositing at least one layer of metallic material into openings defined on a sacrificial substrate. The openings may be within the surface of the substrate, or in one or more layers deposited on the surface of the sacrificial substrate. Each spring contact element has a base end portion, a contact end portion, and a central body portion. The contact end portion is offset in the z-axis (at a different height) than the central body portion. The base end portion is preferably offset in an opposite direction along the z-axis from the central body portion. In this manner, a plurality of spring contact elements are fabricated in a prescribed spatial relationship with one another on the sacrificial substrate. The spring contact elements are suitably mounted by their base end portions to corresponding terminals on an electronic component, such as a space transformer or a semiconductor device, whereupon the sacrificial substrate is removed so that the contact ends of the spring contact elements extend above the surface of the electronic component. In an exemplary use, the spring contact elements are thereby disposed on a space transformer component of a probe card assembly so that their contact ends effect pressure connections to corresponding terminals on another electronic component, for the purpose of probing the electronic component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is division of U.S. patent application Ser. No.11/456,568, filed Jul. 11, 2006) (now U.S. Pat. No. 7,601,039), which isa continuation of U.S. patent application Ser. No. 09/753,310, filedDec. 29, 2000 (now U.S. Pat. No. 7,073,254), which is a division of U.S.patent application Ser. No. 08/802,054, filed Feb. 18, 1997 (now U.S.Pat. No. 6,482,013), which claims the benefit of the following U.S.Patent Application Nos.:

60/034,053 filed 31 Dec. 96;

60/012,027 filed 21 Feb. 96;

60/005,189 filed 17 May 96; and

60/024,555 filed 26 Aug. 96.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to resilient electrical contact(interconnection) elements (structures), also referred to as springcontacts, suitable for effecting pressure connections between electroniccomponents and, more particularly, to microminiature spring contactssuch as may be used in probing (resiliently and temporarily contacting)microelectronic components such as active semiconductor devices.

BACKGROUND OF THE INVENTION

Commonly-owned U.S. patent application Ser. No. 08/152,812 filed 16 Nov.93 (now U.S. Pat. No. 4,576,211, issued 19 Dec. 95), and its counterpartcommonly-owned copending “divisional” U.S. patent application Ser. No.08/457,479 filed 1 Jun. 95 (status: pending) and 08/570,230 filed 11Dec. 95 (status: pending), all by KHANDROS, disclose methods for makingresilient interconnection elements for microelectronics applicationsinvolving mounting an end of a flexible elongate core element (e.g.,wire “stem” or “skeleton”) to a terminal on an electronic componentcoating the flexible core element and adjacent surface of the terminalwith a “shell” of one or more materials having a predeterminedcombination of thickness, yield strength and elastic modulus to ensurepredetermined force-to-deflection characteristics of the resultingspring contacts. Exemplary materials for the core element include gold.Exemplary materials for the coating include nickel and its alloys. Theresulting spring contact element is suitably used to effect pressure, ordemountable, connections between two or more electronic components,including semiconductor devices.

Commonly-owned, copending U.S. patent application Ser. No. 08/340,144filed 15 Nov. 94 and its corresponding PCT Patent Application No.PCT/US94/13373 filed 16 Nov. 94 (WO95/14314, published 26 May 95), bothby KHANDROS and MATHIEU, disclose a number of applications for theaforementioned spring contact element, and also disclosed techniques forfabricating contact pads at the ends of the spring contact elements. Forexample, in FIG. 14 thereof, a plurality of negative projections orholes, which may be in the form of inverted pyramids ending in apexes,are formed in the surface of a sacrificial layer (substrate). Theseholes are then filled with a contact structure comprising layers ofmaterial such as gold or rhodium and nickel. A flexible elongate elementis mounted to the resulting contact structure and can be overcoated inthe manner described hereinabove. In a final step, the sacrificialsubstrate is removed. The resulting spring contact has a contact padhaving controlled geometry (e.g., sharp points) at its free end.

Commonly-owned, copending U.S. patent application Ser. No. 08/452,255filed 26 May 95 and its corresponding PCT Patent Application No.PCT/US95/14909 filed 13 Nov. 95 (WO96/17278, Published 6 Jun. 96), bothby ELDRIDGE, GRUBE, KHANDROS and MATHIEU, disclose additional techniquesand metallurgies for fabricating contact tip structures on sacrificialsubstrates, as well as techniques for transferring a plurality of springcontact elements mounted thereto, en masse, to terminals of anelectronic component (see, e.g., FIGS. 11A-11F and 12A-12C therein).

Commonly-owned, copending U.S. Provisional Patent Application No.60/005,189 filed 17 May 96 and its corresponding PCT Patent ApplicationNo. PCT/US96/08107 filed 24 May 96 (WO96/37332, published 28 Nov. 96),both by ELDRIDGE, KHANDROS, and MATHIEU, discloses techniques whereby aplurality of contact tip structures (see, e.g, #620 in FIG. 6B therein)are joined to a corresponding plurality of elongate contact elements(see, e.g., #632 of FIG. 6D therein) which are already mounted to anelectronic component (#630). This patent application also discloses, forexample in FIGS. 7A-7E therein, techniques for fabricating “elongate”contact tip structures in the form of cantilevers. The cantilever tipstructures can be tapered, between one end thereof and an opposite endthereof. The cantilever tip structures of this patent application aresuitable for mounting to already-existing (i.e., previously fabricated)raised interconnection elements (see, e.g., #730 in FIG. 7F) extending(e.g., free-standing) from corresponding terminals of an electroniccomponent (see. e.g., #734 in FIG. 7F).

Commonly-owned, copending U.S. Provisional Patent Application No.60/024,555 filed 26 Aug. 96, by ELDRIDGE, KHANDROS and MATHIEU,discloses, for example at FIGS. 2A-2C thereof, a technique whereby aplurality of elongate tip structures having different lengths than oneanother can be arranged so that their outer ends are disposed at agreater pitch than their inner ends. Their inner, “contact” ends may becollinear with one another, for effecting connections to electroniccomponents having terminals disposed along a line, such as a centerlineof the component.

The present invention addresses and is particularly well-suited tomaking interconnections to modern microelectronic devices having theirterminals (bond pads) disposed at a fine-pitch. As used herein, the term“fine-pitch” refers to microelectronic devices that have their terminalsdisposed at a spacing of less than 5 mils, such as 2.5 mils or 65 μm. Aswill be evident from the description that follows, this is preferablyachieved by taking advantage of the close tolerances that readily can berealized by using lithographic rather than mechanical techniques tofabricate the contact elements.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved techniquefor fabricating spring contact elements.

Another object of the invention is to provide a technique forfabricating spring contact elements using processes that are inherentlywell-suited to the fine-pitch close-tolerance world of microelectronics.

Another object of the invention is to provide a technique forfabricating spring contact elements that are suitable for probingelectronic components such as semiconductor devices, and that is readilyscaleable to probing fine-pitch peripheral interconnect structures.

Another object of the invention is to provide a technique forfabricating spring contact elements that are suitable for socketingelectronic components such as semiconductor devices, such as forperforming burn-in on said devices.

According to the invention, an elongate spring contact element suitablefor microelectronic applications is fabricated by forming depressions(such as trenches, such as by etching) in a sacrificial substrate anddepositing (such as by plating) metallic materials into the depressions.A plurality of spring contact elements may be fabricated in this manneron a single sacrificial substrate, with lithographically-definedtolerances (e.g., dimensions, spacings).

The resulting spring contact elements may then be mounted to anothersubstrate such as a passive substrate or an active substrate such as asemiconductor device, after which the sacrificial substrate is removed.

An exemplary spring contact element formed in this manner has a length“L” between its base end and its contact end. The base end is preferablyoffset in a first direction from a central portion of the spring contactelement, and the contact end is preferably offset in an oppositedirection from the central portion. In this manner, the overall springcontact element is not planar and, when its base end is mounted to anelectronic component, its contact end extends above the surface of theelectronic component to which it is mounted.

An exemplary sacrificial substrate upon which the spring contactelements may be fabricated is a silicon wafer, in which case the processof the present invention advantageously utilizes the directionallyselective etching of silicon used for micro-machining processes tocreate an electroform which is used to place up the final spring contactelement. This approach may optionally employ laser-based ablation ofphotoresist, as opposed to lithographic development of the photoresist,in order to create the high aspect ratio of width to height which isrequired for fine pitch spacings between the spring contact elements.

An exemplary application for the spring contact elements of the presentinvention is as probe elements used to effect pressure connectionsbetween a substrate and a device-under-test (DUT), in which case thespring contact elements are suitably mounted to a space transformercomponent of a probe card assembly, such as is described in theaforementioned Ser. No. 08/554,902 and PCT/US95/14844. Alternatively,the spring contact elements are mounted to and extend from an activeelectronic component such as an application specific integrated circuit(ASIC).

The spring contact element is suitably formed of at least one layer of ametallic material selected for its ability to cause the resultingcontact structure to function, in use, as a spring (i.e., exhibitelastic deformation) when force is applied to its contact (free) end.

The resulting spring contact element is preferably “long and low”,having:

-   -   a length “L”, as measured from one end to another end;    -   a height “H” measured transverse the length in a direction that        is normal (z-axis) to the surface of the sacrificial substrate        (and, normal to the component to which the spring contact        element is ultimately mounted);    -   a contact end portion which is offset in a one direction (e.g.,        negative along the z-axis) from a central portion of the spring        element by a distance “d1”; and    -   a base end portion which is offset in one direction (e.g.,        positive z-axis) from the central portion of the spring element        by a distance. “d2”.

The spring contact element is preferably tapered from the one (base) endto the other (contact) end thereof, the spring contact element havingthe following dimensions:

-   -   a width “w1” at its base end as measured parallel to the surface        of the sacrificial substrate and transverse to the longitudinal        axis of the spring element;    -   a width “w2” at its contact end as measured parallel to the        surface of the sacrificial substrate and transverse to the        longitudinal axis of the spring element;    -   a thickness “t1” at its base end, measured along the z-axis; and    -   a thickness “t2” at its contact end, measured along the z-axis;        resulting in:    -   a widthwise taper angle “α” (alpha); and    -   a thickness taper angle “β” (beta).

The spring contact element is also suitably provided with a projectingfeature at its contact end, said feature having a dimension “d3”measured along the z-axis.

There is thus described herein an exemplary spring contact elementsuitable for effecting connections between two electronic components,typically being mounted by its base end to a one of the two electroniccomponents and effecting a pressure connection with its contact end(e.g., by the projecting feature) to an other of the two electroniccomponents, having the following dimensions (in mils, unless otherwisespecified):

dimension range preferred L  10-1000 60-100 H 4-40 5-12 d1 3-15 7 ± 1 d20-15 7 ± 1 d3 0.25-5    3 w1 3-20 8-12 w2 1-10 2-8  t1 1-10 2-5  t2 1-101-5  α  0-30° 2-6° β  0-30° 0-6°

Other objects, features and advantages of the invention will becomeapparent in light of the following description thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made in detail to preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. The drawings are intended to be illustrative, not limiting.

Although the invention will be described in the context of thesepreferred embodiments, it should be understood that it is not intendedto limit the spirit and scope of the invention to these particularembodiments.

Certain elements in selected ones of the drawings are illustratednot-to-scale, for illustrative clarity.

Often, similar elements throughout the drawings are referred to bysimilar references numerals. For example, the element 199 may be similarin many respects to the element 299 in another figure. Also, often,similar elements are referred to with similar numbers in a singledrawing. For example, a plurality of elements 199 may be referred to as199 a, 199 b, 199 c, etc.

FIG. 1A is a cross-sectional view of a spring contact element, accordingto the invention.

FIG. 1B is a plan view of the spring contact element of FIG. 1A,according to the invention.

FIG. 1C is a cross-sectional view of an alternate embodiment of a springcontact element, according to the invention.

FIG. 1D is an enlarged cross-sectional view of the spring contactelement of FIG. 1C.

FIG. 1E is a cross-sectional view of an alternate embodiment of a springcontact element, according to the invention.

FIGS. 2A-2I are cross-sectional views of a technique for fabricatingspring contact elements on a sacrificial substrate, according to theinvention.

FIG. 2J is a cross-sectional view of a spring contact element residingon a sacrificial substrate, according to the invention.

FIG. 3A is a cross-sectional view of an alternate embodiment of a springcontact element residing on a sacrificial substrate, according to theinvention.

FIG. 3B is a perspective view of the spring contact element of FIG. 3A,omitting a showing of the sacrificial substrate, according to theinvention.

FIGS. 4A-4B are cross-sectional views illustrating a technique formounting a plurality of spring contact elements which initially areresident on a sacrificial substrate to another component such as a spacetransformer, according to the invention.

FIG. 4C is a cross-sectional view of a plurality of spring contactelements mounted to a component such as a space transformer, in use,probing (making temporary pressure connections with) another componentsuch as a semiconductor device, according to the invention.

FIG. 4D is a cross-sectional view of another embodiment (compare FIG.4B) of a technique for mounting a plurality of spring contact elementsto another component such as a space transformer, according to theinvention.

FIG. 4E is a cross-sectional view of another embodiment (compare FIG.4B) of a technique for mounting a plurality of spring contact elementsto another component such as a space transformer, according to theinvention. This figure also illustrates another embodiment of a springcontact element, according to the invention.

FIG. 4F is a cross-sectional view of another embodiment (compare FIG.4E) of a technique for mounting a plurality of spring contact elementsto another component such as a space transformer, according to theinvention. This figure also illustrates another embodiment of a springcontact element, according to the invention.

FIG. 5 is a schematic (stylized) plan view illustration of anapplication (use) for the spring contact elements of the presentinvention.

FIG. 6 is a schematic (stylized) plan view illustration of anotherapplication (use) for the spring contact elements of the presentinvention.

FIG. 7A is a cross-sectional view of another embodiment (compare. FIG.4D) of a technique for mounting a spring contact element to anothercomponent such as a space transformer, according to the invention.

FIG. 7B is a cross-sectional view of another embodiment (compare FIG.7A) of a technique for mounting a spring contact element to anothercomponent such as a space transformer, according to the invention.

FIG. 7C is a cross-sectional view of another embodiment (compare FIG.7A) of a technique for mounting a spring contact element to anothercomponent such as a space transformer, according to the invention.

FIG. 7D is a cross-sectional view of another embodiment (compare FIG.7A) of a technique for mounting a spring contact element to anothercomponent such as a space transformer, according to the invention.

FIG. 8A is a perspective view of an alternate embodiment of a springcontact element (compare FIG. 3B), omitting a showing of the sacrificialsubstrate, according to the invention.

FIG. 8B is a perspective view of an alternate embodiment of a springcontact element (compare FIG. 8A), omitting a showing of the sacrificialsubstrate, according to the invention.

FIG. 9A is a side cross-sectional view of a first step in a techniquefor achieving controlled impedance in a spring contact element,according to the invention.

FIG. 9B is a side cross-sectional view of a next step in the techniquefor achieving controlled impedance in a spring contact element,according to the invention.

FIG. 9C is an end cross-sectional view of the controlled impedancespring contact element of FIG. 9B, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Commonly-owned, copending U.S. patent application Ser. No. 08/554,902filed 9 Nov. 95 and its corresponding PCT Patent Application No.PCT/US95/14844 filed 13 Nov. 95 (WO96/15458, published 23 May 96), bothby ELDRIDGE, GRUBE, KHANDROS and MATHIEU, disclose a probe card assemblywhich includes elongate resilient (spring) contact elements mounted to a“space transformer” component. As used herein, a space transformer is amultilayer interconnection substrate having terminals disposed at afirst pitch on a one surface thereof and having corresponding terminalsdisposed at a second pitch on an opposite surface thereof, and is usedto effect “pitch-spreading” from the first pitch to the second pitch. Inuse, the free ends (tips) of the elongate spring contact elements makepressure connections with corresponding terminals on an electroniccomponent being probed (e.g., tested).

Elongate, Resilient Cantilever-Like Contact Element

FIGS. 1A and 1B illustrate an elongate resilient (spring) contactelement 100 that is suitable for attachment as a free-standing structureto an electronic component including, but not limited to, the spacetransformer of the aforementioned probe card assembly.

The structure 100 is elongate, has two ends 102 and 104, central portion106 therebetween, and has an overall longitudinal length of “L” betweenthe two ends. The length “L” is in the range of 10-1000 mils, such as40-500 mils or 40-250 mils, preferably 60-100 mils. As will becomeapparent from the discussion that follows, in use the structure has aneffective length of “L”, less than “L”, which is the length over whichthe structure can flex in response to a force applied thereto.

The end 102 is a “base” whereat the contact element 100 will be mountedto an electronic component (not shown). The end 104 is a “free-end”(tip) which will effect a pressure connection with another electroniccomponent (e.g., a device-under-test, not shown). Although notillustrated, it is also possible that the contact element 100 has anelongate “tail” portion extending beyond the base end 102, opposite thecentral portion 106.

The structure 100 has an overall height of “H”. The height “H” is in therange of 4-40 mils, preferably 5-12 mils. (1 mil=0.001 inches)

As best viewed in FIG. 1A, the structure is “stepped”. The base portion102 is at a first height, the tip 104 is at another height, and a middle(central) portion 106 is at a third height which is between the firstand second heights. Therefore, the structure 100 has two “standoff”heights, labelled “d1” and “d2” in the figure. In other words, thespring contact element 100 has two “steps”, a step up from the contactend 104 to the central body portion 106, and a further step up from thecentral body portion 106 to the base end 102.

In use, the standoff height “d1”, which is the “vertical” (as viewed inFIG. 1A) distance between the tip 104 and the central portion 106,performs the function of preventing bumping of the structure (contactelement) with a surface of a component being contacted by the tip end104.

In use, the standoff height “d2”, which is the “vertical” (as viewed inFIG. 1A) distance between the base 102 and the central portion 106;performs the function of allowing the beam (contact element) to bendthrough the desired overtravel.

The dimensions for the standoff heights “d1” and “d2” are

-   -   “d1” is in the range of 3-15 mils, preferably approximately 7        mils+1 mil; and    -   “d2” is in the range of 0-15 mils, preferably approximately 7        mils+1 mil. In the case of “d2” being 0 mil, the structure would        be substantially planar (without the illustrated step) between        the central portion 106 and the base portion 102.

As best viewed in FIG. 1B, the structure 100 is preferably provided witha “joining feature” 110 at its base portion 102. The joining feature maybe a tab or, optionally a stud, which is used to facilitate brazing theprobe structure to a substrate (e.g., a space transformer or asemiconductor device) during assembly therewith. Alternatively, thecomponent or substrate to which the structure 100 is mounted may beprovided with a stud or the like to which the base portion 102 ismounted.

In use, the structure 100 is intended to function as a cantilever beam,and is preferably provided with at least one taper angle, labelled “α”in FIG. 1B. For example, the width “w1” of the structure 100 at its baseend 102 is in the range of 5-20 mils, preferably 8-12 mils, and thewidth “w2” of the structure 100 at its tip end 104 in the range of 1-10mils, preferably 2-8 mils, and the taper angle “α” is preferably in therange of 2-6 degrees. The narrowing of (taper) the structure 100, fromits base 102 to its tip 104, permits controlled flexure and more evenstress distribution (versus concentration) of the structure 100 when itsbase 102 is secured (immovable) and a force is applied at its tip (104).

As will be evident in the discussion presented hereinbelow, the width ofthe structure (hence, the taper angle “α”) is readily controlledemploying well-known lithographic techniques.

The tip end 104 of the structure 100 is preferably provided with anintegral protruding topological feature 108, for example in thegeometric form of a pyramid, to aid in effecting pressure connection toa terminal of an electronic component (not shown).

As illustrated in FIGS. 1A and 1B, the spring contact element 100 isthree-dimensional, extending in the x- y- and z-axes. Its length “L” isalong, the y-axis, its widths (“w1” and “w2”) is along the x-axis, andits thicknesses (“t1” and “t2”) and height (“H”) are along the x-axis.As will become evident in the discussion set forth hereinbelow (see,e.g., FIG. 4B), when the spring contact element 100 is mounted to anelectronic component, it is mounted thereto so that the length and widthof the spring contact element are parallel to the surface of theelectronic component, and its height is normal to the surface of theelectronic component.

FIG. 1C illustrates a contact structure 150 similar in most respects tothe structure 100 of FIGS. 1A and 1B. The structure is elongate, has abase end 152 (compare 102) and a tip end 154 (compare 104), and atopological feature 158 (compare 108) incorporated into its tip end. Theprincipal difference being illustrated in FIG. 1C is that the structurecan be provided with a second taper angle “β”.

As best viewed in FIG. 1C, the thickness “t1” of the structure 100 atits base end 102 is in the range of 1-10 mils, preferably 2-5 mils, andthe thickness “t2” of the structure 100 at its tip end 104 in the rangeof 1-10 mils, preferably 1-5 mils, and the taper angle “β” is preferablyin the range of 2-6 degrees.

The angle “β” (FIG. 1C) may be created using various methods forcontrolling the thickness distribution. For example, if the structure100 is formed by plating, a suitable plating shield can be incorporatedinto the bath. If the structure 100 is formed other than by plating,appropriate known processes for controlling the spatial distribution ofthickness of the resulting structure would be employed. For example,sandblasting or electro-discharge machining (EDM) the structure 100.

Thus, the structure suitably has a composite (dual) taper from its baseend 102 to its tip end 104. It has a taper angle “α” which, as will beevident from the description of a contact structure mounted to acomponent or substrate set forth hereinbelow, is parallel to the x-yplane of the substrate or component to which the contact structure 100is mounted. And it has a has a taper angle “β” which represents anarrowing of the structure's cross section (z-axis).

It is within the scope of this invention that the structure is nottapered in width, in which case the taper angle “α” would be ZERO. It isalso within the scope of this invention that the taper angle “α” isgreater than 2-6 degrees, for example as much as 30 degrees. It iswithin the scope of this invention that the structure is not tapered inthickness, in which case the taper angle “β” would be ZERO. It is alsowithin the scope of this invention that the taper angle “β” is greaterthan 2-6 degrees, for example as much as 30 degrees. It is within thescope of this invention that the structure (contact element) is taperedonly in thickness and not in width, or only in width and not inthickness.

It is within the scope of this invention that the contact element istapered to be wider and/or thicker at its contact end 104 than at itsbase end 102, rather than narrower and/or thinner as described above. Itis also possible that the contact element is provided with a pluralityof different tapers, for example, tapering in (e.g., wider to narrower)from the base end to the central portion, then tapering back out (e.g.,narrow to wider) towards the contact end.

The contact structures 100 and 150 are principally, preferably entirely,metallic, and may be formed (fabricated) as multilayer structures, as isdescribed in greater detail hereinbelow. Suitable materials for the oneor more layers of the contact structures include but are not limited to:

nickel, and its alloys;

copper, cobalt, iron, and their alloys;

gold (especially hard gold) and silver, both of which exhibit excellentcurrent-carrying capabilities and good contact resistivitycharacteristics;

elements of the platinum group;

noble metals;

semi-noble metals and their alloys, particularly elements of thepalladium group and their alloys; and

tungsten, molybdenum and other refractory metals and their alloys.

In cases where a solder-like finish is desired, tin, lead, bismuth,indium and their alloys can also be used.

FIG. 1D shows an enlarged view of the contact end 154 of the contactstructure 150 (equally applicable to the contact ends of other contactstructures illustrated herein). In this enlarged view it can be seenthat the contact feature 154 is suitably quite prominent, projecting adistance “d3”, in the range of 0.25-5 mils, preferably 3 mils from thebottom (as viewed) surface of the contact end of the spring contactelement, and is suitably in the geometric shape of a pyramid, atruncated pyramid, a wedge, a hemisphere, or the like.

The resulting spring contact element has an overall height “H” which isthe sum of “d1”, “d2” (and “d3”) plus the thickness of the central bodyportion.

There has thus been described a exemplary spring contact elementsuitable for effecting connections between two electronic components,typically being mounted by its base end to a one of the two electroniccomponents and effecting a pressure connection with its contact end toan other of the two electronic components, having the followingdimensions (in mils, unless otherwise specified):

dimension range preferred L  10-1000 60-100 H 4-40 5-12 d1 3-15 7 ± 1 d20-15 7 ± 1 d3 0.25-5    3 w1 3-20 8-12 w2 1-10 2-8  t1 1-10 2-5  t2 1-101-5  α  0-30° 2-6° β  0-30° 0-6°from which the following general relationships are evident:

“L” is approximately at least 5 times “H”;

“d1” is a small fraction of “H”, such as between one-fifth and one-halfthe size of “H”;

“w2” is approximately one-half the size of “w1”, and is a small fractionof “H”, such as between one-tenth and one-half the size of “H”; and

“t2” is approximately one-half the size of “t1”, such as betweenone-tenth and one-half the size of “H”.

Another dimension is of interest—namely, the width and length (i.e.,footprint) of the overall tip end (104). In instances where the tip endis expected to make contact with a terminal of an electronic componentwhich is recessed (e.g., a bond pad of a semiconductor device which haspassivation material surrounding the bond pad), it may be desirable toensure that the footprint of the tip end is sufficiently small to makesuch contact. For example, less than 4 mils by 4 mils). Else, it must beensured that the contact feature (108) is of sufficient height (d3) tomake contact with the recessed terminal. Generally speaking, theselection of an appropriate tip end design will be dictated by thepeculiarities of the given application. For example, for contacting bondpads on silicon devices, the tip end design illustrated in FIG. 1D wouldlikely be most appropriate. For contacting C4 bumps, the tip end designillustrated in FIG. 1E (described hereinbelow) would likely be mostappropriate.

FIG. 1E illustrates an alternate embodiment of the invention whereindiscrete contact tip structures 168, such as are described in theaforementioned PCT/US96/08107 can be mounted to the contact end portions164 of the spring contact elements, such as by brazing 170 thereto. Thisprovides the possibility of the contact tip structure 168 having adifferent metallurgy, than the spring contact element (150). Forexample, the metallurgy of the spring contact element (150) is suitablytargeted at its mechanical (e.g., resilient, spring) characteristics andits general capability to conduct electricity, while the metallurgy of acontact tip structure 168 mounted thereto is appropriately targeted tomaking superior electrical connection with a terminal (see, e.g., 420,hereinbelow) of an electronic component (see, e.g., 422, hereinbelow)being contacted and, if needed, can have superior wear-resistance.

Fabricating the Contact Structure

A contact element such as that described hereinabove would be difficult,to punch out of a foil of spring material and mount in a preciselocation on an electronic component such as a space transformer, at thescale (dimensions) described herein.

According to an aspect of the invention, processes such asphotolithography are employed to fabricate the spring contact elementsof the present invention with tolerances, both of the springs themselvesand with regard to the relative locations of a plurality of springs,suitable for use as interconnections in the context of fine-pitchmicroelectronics.

FIGS. 2A-2J illustrates an exemplary process 200 for fabricating theaforementioned resilient contact structures 100 (150). The presentinvention is not limited to this exemplary process.

As illustrated in FIG. 2A, commencing with a suitable sacrificialsubstrate 202, such as a silicon wafer, a blanket layer 204 of siliconnitride (“nitride”) is applied to the surface of the sacrificialsubstrate. This layer 204 will act as an etch stop in subsequent stepsof the process. A layer 206 of a masking material, such as photoresist,is applied over the nitride layer 204, and is imaged and developed usingconventional photolithographic techniques (e.g., actinic light passingthrough a mask).

It is within the scope of this invention that the sacrificial substrateis a material selected from the group consisting of silicon, aluminum,copper, ceramic, and the like. For example, silicon in the form of asilicon semiconductor wafer. Or aluminum or copper in the form of a foilor sheet. Or, aluminum or copper in the form of a layer on anothersubstrate. The sacrificial substrate can also be a “clad” (multilayer)structure, such as copper-invar-copper or aluminum-alumina-aluminum, andpreferably has a coefficient of thermal expansion which matches that ofthe component to which the contact structures are ultimately mounted.The example set forth herein, vis-a-vis the “machining” of thesacrificial substrate is applicable to sacrificial substrates which aresilicon. One of ordinary skill in the art to which the present inventionmost nearly pertains will readily understand how to achieve comparableresults with sacrificial substrates formed of other (than silicon)materials. It is within the scope of this invention that the sacrificialsubstrate can be formed of titanium-tungsten which is readily etchedwith hydrogen peroxide.

Using conventional chemical etching techniques, an opening 210 to thesurface of the sacrificial substrate 202 can be created through both ofthe layers 206 and 204, as illustrated in FIG. 2C. In the area of theopening 210, the surface of the sacrificial substrate is exposed. Thesurface of the sacrificial substrate is covered by the residual(remaining) portions 204 a and 206 a of the layers 204, 206,respectively, that are not removed by etching.

Alternatively, as illustrated in FIG. 2B, selected portions of thephotoresist 206 can be removed employing other techniques, such as knowntechniques involving lasers, E-beam, and the like, and the resultingexposed (no longer covered) portions of the nitride layer 204 can beremoved using chemical etching processes, the result of which is that anopening 210 to the surface of the sacrificial substrate 202 can becreated, as illustrated in FIG. 2C. Using a laser to remove portions ofthe masking layer 206 (other portions 206 a being remaining portions)provides the possibility of having more carefully-controlled aspectratios for the resulting openings 210, for example, obtaining steeperand deeper, more-vertical sidewalls in the opening.

In a next step of the process 200, illustrated in FIG. 2D, thesacrificial substrate 202 is etched in the openings 210 through thenitride layer 204, using known chemistry for selectively etching thesubstrate. For example, a silicon substrate can selectively be etched(with respect to nitride) using potassium hydroxide (KOH). This willcreate a trench 220 in the substrate 202, the depth of which iscontrolled to correspond to the aforementioned standoff height “d2” (seeFIG. 1A). Also, in the case of employing a silicon wafer as thesubstrate 202, the sidewall 222 of the trench will favorably exhibit anon-vertical angle “θ”, such as 54.74° (rather than)90°, as may beinherent in and controlled by the crystalline structure of thesubstrate. For example, a silicon substrate having a (100) crystalorientation when etched will etch in the (111) planes.

After creating the trench 220, the residual portion 204 a of the etchstop layer 204 is preferably removed.

In a next step of the process 200, illustrated in FIG. 2E, the previoussteps illustrated and described with respect to FIGS. 2A-2D arerepeated, to create another trench 230 in the sacrificial substrate 202that is longitudinally offset from and contiguous with the trench 220.Alternatively, the trench 230 can be formed in an end portion (righthand side, as viewed) of the previously-formed trench 220. In otherwords, an etch stop layer 224 (compare 204) is applied, a masking layer(not shown, compare 206) is applied over the etch stop layer, an openingis created through the masking layer and the etch stop layer, and thesubstrate is etched. This will result in a trench 230 in the substrate202, the depth of which is controlled to correspond to theaforementioned standoff height “d1” (see FIG. 1A). Also, as mentionedhereinabove, in the case of employing a silicon wafer as the substrate202, the sidewall 232 of the trench 230 will favorably be “angled”,rather than vertical.

In a next step of the process 200, illustrated in FIG. 2F, the previoussteps illustrated and described with respect to FIGS. 2A-2D arerepeated, to create a small geometric intrusion (depression) 240(compare “d3” of FIG. 1D) in the sacrificial substrate 202 in the bottomof the second trench 230. (The term “intrusion” is selected as being thecomplement to “negative of” the resulting protruding feature (108) thatwill be fabricated on the resulting spring contact element. The feature240 could also be considered to be a “depression”, a “recess”, an“indentation” or an “intaglio”.) Namely, an etch stop layer 234 (compare204, 224) is applied, a masking layer (not shown, compare 206) isapplied over the etch stop layer, a small opening is created through themasking layer and the etch stop layer, and the substrate is etched. Theshape of the intrusion 240 is suitably that of an inverted (as viewed)pyramid and, as mentioned hereinabove, may suitably have sides at thecrystalline angle of silicon. As will be evident from the descriptionhereinbelow, this intrusion 240 will define the topological feature 108present on the tip of the contact structure 100 described hereinabove(pyramid, truncated pyramid, etc.). Finally, the nitride layer 234 isremoved.

Each of the trenches 220 and 230 can be considered to be a “subtrench”of a larger overall trench which also includes the depression 240.

The steps described in FIGS. 2A-2F describe the preparation of asacrificial substrate for the fabrication of resilient contactstructures thereon. It is within the scope of this invention thatcertain of the steps described hereinabove could be performed in otherthan the recited order. For example, the trench 230 could be formedprior to forming the trench 220.

It bears mention here that it is within the scope of this invention thatthe process described hereinabove could be carried out on a siliconwafer that has active devices already formed therein. However, as isevident, the forming of trenches (220 and 230) and features (240) couldwell destroy the active devices unless (i) they were to be formed atareas of the wafer that do not contain active devices, or (ii) thespring contact elements were fabricated on a sacrificial substrate thenattached to active devices (see e.g., FIGS. 4A-4B hereinbelow), or (iii)a layer of material suitable for performing the function of thesacrificial substrate (202) described hereinabove is first applied tothe surface of the wafer.

As described hereinabove, the sacrificial substrate has been preparedwith a first trench 220 which is lower than (extends into) the surfaceof the substrate, a second trench 230 which is lower than (extendsdeeper into) and is contiguous (end-to-end) with the first trench 220,and an intrusion (negative projection, depression) 240 within the secondtrench 230 which extends yet deeper into the substrate. Contact elementswill be fabricated in these trenches, then will need to be “released”from the trenches.

In a next step of the process 200, illustrated in FIG. 2G, one or moremetallic layers are blanket deposited, such as by sputtering, onto thesubstrate 202. For example, a layer 252 of aluminum followed by a layer254 of copper. Exemplary thicknesses for these layers are:

-   -   5000-50,000 Å preferably 20,000 Å for the first layer 252; and    -   1000-50,000 Å, preferably 5,000 Å for the second layer 254.

The purposes of these layers 252 and 254 are generally:

-   -   the first layer 252 is a material (such as aluminum) selected        for its eventual use as a “release” layer (described        hereinbelow); and    -   the second layer 254 serves as a “seed” layer for deposition of        a subsequent layer (256, described hereinbelow) and, in the case        of a previous aluminum layer 252, will prevent the subsequent        layer 256 from “smutting” as a result of removing the previous        “release” layer 252. This layer may be removed from the final        spring contact element and may act as a protective “capping”        layer during the release process.

Together, the layers 252 and 254 constitute a “release mechanism” whichis incorporated into the sacrificial substrate which, in use, permitsthe sacrificial substrate to be removed after the spring contactelements fabricated thereon (as described hereinbelow) are mounted tothe terminals of the electronic component.

Metallic materials forming the resulting contact structures (100, 150)can be deposited into the trenches and features formed therein by anysuitable technique including, but not limited to: various processesinvolving deposition of materials out of aqueous solutions; electrolyticplating; electroless plating; chemical vapor deposition (CVD); physicalvapor deposition (PVD); processes causing the deposition of materialsthrough induced disintegration of liquid or solid precursors; and thelike, all of these techniques for depositing materials being generallywell known. Electroplating is a generally preferred technique.

Next, as illustrated in FIG. 2H, a masking layer 258 (compare 206), suchas photoresist, is applied to the substrate and is patterned to have anopenings 260 corresponding to the length “L” and width (“w1” and “w2”,and widths therebetween) of the desired resulting spring contact element(see FIGS. 1A and 1B). A relatively thick “structural” metallic layer256 is deposited within the openings 260, using any suitable processsuch as electroplating of a suitable material such as nickel, atop thepreviously applied layers 252 and 254. This layer 256 is intended tocontrol (dominate) the mechanical characteristics of the resultingspring contact element (100). The opening 260 includes the trench 220,the trench 230, the depression 240 and a portion of the substrate 202which is adjacent and contiguous with the first trench 220.

An exemplary average ((t1+t2)/2) thickness for this layer 256 is 1-10mils, preferably 1-5 mils. Suitable materials for the layer 256, such asnickel and its alloys, have been set forth hereinabove.

It is within the scope of this invention that additional layers may beincluded in the build-up of the contact structure. For example, prior todepositing the layer 256, a layer of a material selected for itssuperior electrical characteristics of electrical conductivity, lowcontact resistance, solderability, and resistance to corrosion may bedeposited. For example, gold or rhodium (both of which are excellentcontact materials), nickel-cobalt (a good material for brazing), gold(another good material for brazing), and the like.

In a next step of the process 200, illustrated in FIG. 2I, the maskinglayer 258 is removed, exposing the layers 252 and 254. These layers aresuitably selectively chemically etched, so that all that remains on thesubstrate is an elongate structure 270 (compare 100) having a one end272 (compare 102), an other end 274 (compare 104), a central portion 276(compare 106) and a raised topological feature 278 (compare 108) at itsend 274. This elongate structure 270 is the resulting spring contactelement.

FIG. 2J is another cross-sectional view of the resulting structure 270,still resident upon the substrate, with the layers 252 and 254 omitted,for illustrative clarity. The similarity between this structure 270 andthe spring contact element 100 of FIG. 1A is readily apparent.

One having ordinary skill in the art to which the present invention mostnearly pertains will recognize that the processes described hereinabovecan readily be performed at a plurality of locations on a sacrificialsubstrate to result in a plurality of contact structures (270) havingbeen fabricated at a plurality of precisely-controlled predeterminedlocations on the substrate 202. The process has been described withrespect to one exemplary structure 270 being fabricated at one location,for purposes of illustrative clarity.

It is within the scope of this invention that rather than patterning asacrificial substrate to have a plurality of trenches, eachcorresponding to a single resulting contact element, that a sacrificialsubstrate can be prepared with a single very wide set of trenches, (220,230, 240), then deposit the metals (252, 254, 256), then perform anadditional final masking and etching step to define the individualcontact elements. Such a process would look similar to the processdescribed hereinabove with respect to FIGS. 2A-2G, followed by blanketdeposition of the metal (256) layers, followed by masking and etching todefine the individual contact elements.

An Alternate Embodiment

FIGS. 3A and 3B illustrate another one of many possible embodiments fora contact structure 300 fabricated by the techniques describedhereinabove. Instead of a flat connection tab (see 110), a somewhattruncated-pyramidal joining feature (stud) 310 is fabricated as anattachment feature at the base portion 304 of the contact structure 300.When the contact structure 300 is mounted to a substrate, such as aspace transformer, this stud 310 will allow for some misalignmenttolerance during assembly. The remaining portions of the contactstructure 300 are comparable to those described hereinabove with respectto the contact structure 270-namely, a central main body portion 306(compare 276), a contact end portion 304 (compare 274), and a feature308 (compare 278).

Thus, there has thus been shown an exemplary process for fabricatingelongate resilient (spring) interconnection (contact) elements on asacrificial substrate. This can be considered to be an “interim”product, awaiting further use, as follows:

Alternative A: These spring contact elements can simply be removed fromthe sacrificial substrate, resulting in a “bucket of springs” which maybe attached, such as with automated equipment, to an electroniccomponent, although the benefit of having lithographically (i.e., tovery close tolerances) located the plurality of spring contact elementswith respect to one another would be lost.

Alternative B: A more “viable” technique for installing the springcontact elements onto an electronic component, involving removing thesacrificial substrate after the contact structures resident thereon aremounted (by the base ends) to an electronic component or to a substrate,is described hereinbelow with respect to FIGS. 4A-4C.

Removing the Sacrificial Substrate

With regard to either of the alternatives (“A” or “B”, set forthhereinabove, a suitable mechanism must be employed for removing thesacrificial substrate (i.e, releasing the fabricating contact elementsfrom the sacrificial substrate whereupon they reside). Exemplarysuitable mechanisms include, but are not limited to:

-   -   chemically etching to release the contact structures (e.g., 270)        from the sacrificial substrate (202). As mentioned above, the        aluminum layer 252 is readily selectively etched to cause        separation of the contact structure 270 from the substrate 202.        (The copper layer 254 helps prevent contamination of the layer        256 in such a process, and may ultimately be etched from the        separated contact structure 270.)    -   in lieu of the aluminum and copper layers described hereinabove,        employing layers of materials that are non-wetting with respect        to one another and/or that ball up when heated (e.g., lead,        indium, tin), then heating the substrate 202 to cause the        contact structures 270 to be released therefrom.

Mounting the Contacts to a Substrate

As mentioned hereinabove, a plurality of contact structures (e.g., 270)fabricated upon a sacrificial substrate (e.g., 202) can be mounted(affixed) to another substrate or to an electronic component such as aspace transformer.

FIG. 4A illustrates a technique 400 wherein a plurality (two of manyshown) of contact structures 402 (compare 100, 150, 270, 300) have beenfabricated on a sacrificial substrate 404 (compare 202). The base endportions (compare 310) of the contact structures 402 are brought intocontact with a corresponding plurality of terminals 406 on an electroniccomponent 408 such as the aforementioned space transformer of a probecard assembly, whereupon the base end portions are suitably soldered orbrazed 410 to the terminals 406.

It is within the scope of this invention that any suitable techniqueand/or material for affixing the base end portions of the contactstructures (402) to terminals of an electronic component be employed,including brazing, welding (e.g., spot welding), soldering, conductiveepoxy, tacking the contact structure in any suitable manner to theterminal and securely affixing the contact structure to the terminal byplating (e.g., electroplating), and the like.

The sacrificial substrate 404 is now removed, in any suitable mannersuch as those described hereinabove (e.g., chemical etching, heating),resulting in an electronic component (408) having spring contactelements (402) affixed thereto, as illustrated in FIG. 4B.

As is evident in FIG. 4B, a plurality of elongate spring contactelements can be mounted to an electronic component having a plurality ofterminals on a surface thereof. Each spring contact element has a baseend and a contact end opposite the base end, and is mounted by its baseend to a corresponding terminal of the electronic component. The contactend of each spring contact element extends above the surface of theelectronic component to a position which is laterally offset from itsbase end.

As mentioned hereinabove, when mounted, the contact structure 402(compare 100) has an “effective” length of “L1”, this being the lengthbetween the tip feature (compare 108) and the inwardmost positionwhereat the base end (compare 102) is affixed to the component 408. The“effective” length represents the length over which the contactstructure can deflect in response to compressive forces applied at thetip end thereof (e.g., at the tip feature).

FIG. 4C illustrates an application for the spring contact elements(resilient contact structures) of the present invention wherein thespring contact elements have been mounted in the manner described withrespect to FIG. 4B to a space transformer component (408) of a probecard assembly (not shown) so that the contact features (compare 308) attheir contact ends (compare 304) make pressure connections withterminals 422 of an electronic component 420 such as a semiconductordevice, or an area of a semiconductor wafer (not shown) containing aplurality of semiconductor devices. As described hereinabove, withrespect to FIG. 1E, it is within the scope of this invention thatseparate and discrete contact tip structures 168) be affixed to thecontact end portions of the spring contact element.

It is within the scope of this invention that the substrate (component)to which the structures 402 are mounted, for example the component 408illustrated in FIG. 4C are active components, such as ASICs.

It is also within the scope of the invention, as is illustrated in FIG.4C, that the component or substrate to which the structures (e.g., 402)are mounted can be provided with a contiguous (as illustrated) orsegmented ground plane to control impedance. Such a ground plane maycomprise a plurality of ground lines 412 aligned directly underneath thestructures 402, but sufficient clearance for the tip of the structure todeflect must be assured. Alternatively, the ground plane 412 can becovered with an insulating layer. Another approach would be to disposeground plane lines 414 on the surface of the substrate 408 slightly(such as 1 mil, in the x-axis) offset from directly underneath thestructures 402, and laying parallel to the structure.

FIG. 4D illustrates an alternate embodiment 440 of the present inventionwherein a cavity (trench) 442 is been formed in the surface of thesubstrate or component 444 (compare 408) to which the contact structures450 (compare 402) have been mounted. The trench 442 is located so thatit is underneath at least the contact end portion 454 (compare 104) ofthe contact structure, and preferably extends underneath a substantialportion of the contiguous central body portion 456 (compare 106) of thespring contact element. The trench extends of a depth “d4” within thesubstrate 444 a suitable distance to allow for a greater range ofdeflection of the contact end portion 454 when, in use, it is urgedagainst an electronic component (see, e.g., FIG. 4C). In FIG. 4D, onetrench 442 is illustrated extending under a plurality (two of manyshown) spring contact elements. It is within the scope of this inventionthat there is a single discrete trench under each of the plurality ofspring contact elements (450) structures mounted to an electroniccomponent (444).

FIG. 4E illustrates an alternate embodiment of the present inventionwherein a spring contact element 460 is mounted to an electroniccomponent 470 (compare 444) via a stud 472 extending from a surface ofthe electronic component 470. The base end 462 of the spring contactelement 460 is suitably brazed to the stud 472. The stud 472 suitablyhas a height in the range of 3-4 mils.

FIG. 4E also illustrates an alternate embodiment of the presentinvention wherein the spring contact element 460 is formed with but asingle step or offset (rather than two steps). As illustrated herein,the offset of the base end portion 462 from the central body portion 466(compare “d2” in FIG. 1A) is ZERO. In other words, in this example, thebase end portion 462 is coplanar with the central body portion 466.Since there is no offset at the base end portion, the base end 462 ismounted to a stud 472 on the surface of the electronic component 470 sothat the body portion 466 is elevated above the surface of the component470. The contact end portion 464 (compare 104) preferably remains offsetby a distance “d1” from the central body portion 466. As suggested bythis figure, many of the variations (alternate embodiments) of thepresent invention can be combined (mixed and matched) to arrive at adesired arrangement of spring contact elements affixed to an electroniccomponent.

FIG. 4F illustrates another embodiment of the invention wherein thespring contact element (contact structure) 480 is formed without anystep or offset (rather than one or two steps). As in the previousexample, the offset of the base end portion 482 from the central bodyportion 486 (compare “d2” in FIG. 1A) is ZERO, and the base end portion482 is coplanar with the central body portion 486. Since there is nooffset at the base end portion, the base end 482 is mounted to a stud492 on the surface of the electronic component 490 so that the bodyportion 486 is elevated above the surface of the component 490. Also,the offset of the contact end portion 484 (compare 104) from the centralbody portion 486 (compare “d1” in FIG. 1A) is ZERO, and the contact endportion 484 is coplanar with the central body portion 486. Since thereis no offset at the contact end portion, a prefabricated contact tipstructure 488 (compare 168) may be affixed (e.g., joined, such as bybrazing) to the contact end 484 so that the body portion 486 will bespaced away from a component (not shown, compare 420) being contacted bythe contact structure 480.

Probe Applications

FIG. 5 illustrates an application wherein a plurality of spring contactelements 500 such as those described hereinabove are arranged on asubstrate such as a space transformer, and affixed thereto in the mannerdescribed hereinabove, so that their contact ends are disposed in amanner suitable for making contact with the bond pads of a semiconductordevice having its bond pads arranged along its periphery.

Each contact element 500 (compare 100) has a base end 502 (compare 102)and a contact end 504 (compare 104), and are mounted to an electroniccomponent such as a space transformer component (schematicallyillustrated by the dashed line 510) of a probe card assembly. Thecontact ends 504 are arranged close to one another, in a patternmirroring that of the bond pads 522 (illustrated schematically bycircles) of an electronic component (schematically illustrated by thedashed line 520) such as a semiconductor device. The spring contactelements 500 “fan-out” from their contact ends 504, so that their baseends 502 are disposed at a greater pitch (spacing from one another) thantheir contact ends 504.

FIG. 6 illustrates another application wherein a plurality of springcontact elements 600 such as those described hereinabove are arranged ona substrate such as a space transformer, and affixed thereto in themanner described hereinabove, so that their contact ends are disposed ina manner suitable for making contact with the bond pads of asemiconductor device having its bond pads arranged in a row along acenterline thereof.

Each spring contact element (compare 100), generally denoted by thereference numeral 600, has a base end 602 (compare 102) and a contactend 604 (compare 104), and are mounted to an electronic component suchas a space transformer component (schematically illustrated by thedashed line 610) of a probe card assembly (not shown). The contact ends604 are arranged close to one another, in a pattern mirroring that ofthe bond pads 622 (illustrated schematically by circles) of anelectronic component (schematically illustrated by the dashed line 620)such as a semiconductor device. The spring contact elements 600 arearranged in the following sequence:

-   -   a first spring contact element 600 a is relatively short (e.g.,        has a length of 60 mils), and is disposed to extend towards a        one side (right, as viewed) of the electronic component 620;    -   a second spring contact element 600 b, adjacent the first spring        contact element 600 a, is also relatively short (e.g., has a        length of 60 mils), and is disposed to extend towards an        opposite side (left, as viewed) of the electronic component 620;    -   a third spring contact element 600 c, adjacent the second spring        contact element 600 b, is relatively long (e.g., has a length of        80 mils), and is disposed to extend towards the one side (right,        as viewed) of the electronic component 620; and    -   a fourth spring contact element 600 d, adjacent the third spring        contact element 600 c, is also relatively long (e.g., has a        length of 80 mils), and is disposed to extend towards the        opposite side (left, as viewed) of the electronic component 620.        In this manner, the contact ends 604 are disposed at a        fine-pitch commensurate with that of the bond pads 622, and the        base ends 602 are disposed at a significantly greater pitch from        one another.

The showing of only two different-length contact structures is merelyexemplary and it should be understood that it is within the scope ofthis invention that a plurality of spring contact elements having morethan two different lengths can be disposed on a common substrate. Theshowing of only two different-length contact structures is merelyexemplary.

It is within the scope of this invention that the techniques illustratedin FIGS. 5 and 6 may be used to generate a plurality of probes (springcontact elements) in any arrangement required for probing of eitherperipheral or lead-on-center (LOC) devices.

Additional Features and Embodiments

In cases where there are a plurality of spring contact elements mountedto a substrate and they are of different lengths (see, e.g., FIG. 6),and assuming that the cross-sections and metallurgy of the springcontact elements are the same as one another, the different lengthspring contact elements will evidently exhibit different reactive forces(spring constants, k).

It is therefore within the scope of this invention that the springconstants of a plurality of spring elements exhibiting different springconstants can be adjusted (tailored), on an individual basis, to makethem more uniform with one another.

FIG. 7A illustrates a technique for tailoring spring constant. In thisexample, a spring contact element 700 (compare 450) is mounted by itsbase end 702 (compare 452) to an electronic component 710 (compare 444).A trench 712 (compare 442) is formed in the surface of the electroniccomponent 710 and extends from under the contact end 704 (compare 454)of the spring contact structure 700, along the body portion 706 (compare456) thereof, towards the base end 702 of the spring contact element 700to a position (point) “P” which is located a prescribed, fixed distance,such as 60 mils from the contact end 704. When a force is applieddownwards to the contact end 704, the entire spring contact element 700will bend (deflect) until the body portion 706 contacts the end of thetrench 712 at the point “P”, whereupon only the outermost portion (fromthe point “P” to the end 704) of the spring contact element is permittedto deflect. The outermost portion of the spring contact element has an‘effective’ length of “L1”. The outermost portion of the spring contactelement has an ‘effective’ length of “L1”. In this manner, the reactionto applied contact forces can be made uniform among spring contactelements of various lengths (so long as the point “P” falls somewherewithin the central body portion of the spring contact element).

FIG. 7B illustrates another technique for tailoring spring constant. Inthis example, a spring contact element 720 (compare 450) is mounted byits base end 702 (compare 452) to an electronic component 710 (compare444). A structure 732 (compare 712) is formed on the surface of theelectronic component 730 (compare 710) at a location between the baseend 722 of the spring contact structure 720, between the surface of theelectronic component 730 and the central body portion 726 (compare 706)of the spring contact element 720 and extends along the body portion 726(compare 706) thereof, towards the contact end 724 of the spring contactelement 720 to a position (point) “P” which is located a prescribed,fixed distance, such as the aforementioned (with respect to FIG. 7Aprescribed distance, from the contact end 724. The structure is suitablya bead of any hard material, such as glass or a pre-cut ceramic ring,disposed on the surface of the electronic component 730. When a force isapplied downwards to the contact end 724, only the outermost portion(from the point “P” to the end 724) of the spring contact element ispermitted to deflect. As in the previous embodiment, the reactions toapplied contact forces can be made uniform among spring contact elementsof various lengths.

FIG. 7C illustrates yet another technique for tailoring spring constant.In this example, a spring contact element 740 (compare 720) is mountedby its base end 742 (compare 722) to an electronic component 750(compare 730). An encapsulating structure 752 (compare 732) is formed onthe surface of the electronic component 750 in a manner similar to thestructure 732 of the previous embodiment. However, in this case, thestructure 752 fully encapsulates the base end 742 of the spring contactstructure 740 and extends along the body portion 746 (compare 726)thereof, towards the contact end 744 thereof, to a position (point) “P”Which is located a prescribed, fixed distance, such as theaforementioned (with respect to FIG. 7B prescribed distance, from thecontact end 744. The outermost portion of the spring contact element hasan ‘effective’ length of “L1”. As in the previous embodiment, when aforce is applied downwards to the contact end 744, only the outermostportion (from the point “P” to the end 744) of the spring contactelement is permitted to deflect. As in the previous embodiment, thereactions to applied contact forces can be made uniform among springcontact elements of various lengths.

FIG. 7D illustrates yet another technique for tailoring spring constant.In this example, a spring contact element 760 (compare 740) is mountedby its base end 762 (compare 742) to an electronic component 770(compare 750). In this example, the body portion 766 is formed with a“kink” 772 at a position (point) “P” which is located a prescribed,fixed distance, such as the aforementioned (with respect to FIG. 7Cprescribed distance, from the contact end 764. The outermost portion ofthe spring contact element has an ‘effective’ length of “L1”. As in theprevious embodiment, when a force is applied downwards to the contactend 744, only the outermost portion (from the point “P” to the end 744)of the spring contact element is permitted to deflect. (The kink 772 canbe sized and shaped so that the entire contact structure deflectsslightly before the kink 772 contacts the surface of the component 770,after which only the outermost portion of the spring element willcontinue to deflect.) As in the previous embodiment, the reactions toapplied contact forces can be made uniform among spring contact elementsof various lengths.

It is within the scope of this invention that other techniques can beemployed to “uniformize” the spring constants among contact elementshaving different overall lengths (“L”). For example, their widths and or“α” taper can be different from one another to achieve this desiredresult.

Alternate Embodiment

The spring contact elements illustrated and described hereinabove havebeen elongate and linear (disposed along the y-axis), generally bestsuited to accommodate movement (deflection) in the z-axis (i.e., normalto the component or substrate to which they are mounted).

It is within the scope of this invention that additional“dimensionality” and commensurate additional freedom of movement beincorporated into the resulting spring contact element.

FIG. 8A illustrates a spring contact element 800 that has beenfabricated according to the techniques set forth hereinabove, with theexception (noticeable difference) that the central body portion 806(compare 106) of the contact element is not straight, Although it maystill lay in a plane (e.g., the x-y plane), it is illustrated as joggingalong the x-axis while traversing the y-axis, in which case the base end802 (compare 102) will have a different x-coordinate than the contactend 804 (compare 104) or the contact feature 808 (compare 108) disposedat the contact end 804.

FIG. 8B illustrates a spring contact element 850 that is similar in manyrespects to the spring contact element 800 of FIG. 8A, with theexception that there is a step between the central body portion 856(compare 806) and the base portion 852 (compare 802) in addition to thestep between the central portion 856 and the contact end portion 854(compare 804). The contact element 850 is illustrated with a contactfeature 858 (compare 808) at its contact end 854.

Controlled Impedance

For use in probing semiconductor devices, particularly at speed testing,it is advantageous that the spring contact element have controlledimpedance.

FIGS. 9A-9C illustrate a technique 900 for achieving controlledimpedance in a spring contact element, according to the invention.

In a first step, best viewed in FIG. 9A, a spring contact element 900(compare 700) is mounted by its base end 902 (compare 702) to a terminal912 of an electronic component 910 (compare 710) such as a spacetransformer component of a probe card assembly. The contact tip end 904(compare 704) is elevated above the surface of the component 9140 and isillustrated as having a contact feature. The spring contact structurehas a central body portion 906 (compare 706) between its base and tipends.

In a next step, best viewed in FIG. 9B, the tip end 904 of the springcontact element is masked (not shown), and a suitable thin (e.g., 1-10μm) insulating layer 920, such as parylene, is deposited, such as byvapor deposition, onto all but the tip end 904 of the spring contactelement, and adjacent surface of the electronic component.

In a next step, best viewed in FIG. 9B, while the tip end 904 of thespring contact element is still masked (not shown), a suitable thin(e.g., less than 0.25 mm) layer 922 of conductive material, such as anyof the conductive metal material described herein, is deposited, such asby sputtering, onto all but the tip end 904 of the spring contactelement, and adjacent surface of the electronic component. Finally, thetip end 904 is unmasked. This results in the central body portion 906 ofthe spring contact element being enveloped by a conductive layer 922,with an insulating layer 920 therebetween.

The conductive layer 922 is suitably connected to ground to function asa ground plane and control the impedance of the resulting spring contactelement. For example, as best viewed in FIG. 9B, the component 910 isprovided with a second terminal 914 which is electrical ground. Thisterminal 914 is suitably masked along with the tip end 904 of the springcontact element prior to applying the insulating layer 920, so that thesubsequent conductive layer 922 will also deposit thereon and beconnected thereto.

Evidently, this thicknesses of the layers 920 and 922 need only besufficient to be continuous, and to provide the sought after controlledimpedance, and should not be so thick as to interfere with themechanical operation of the spring contact element. The representationsin FIGS. 9B and 9C are not drawn to scale.

Although the invention has been illustrated and described in detail inthe drawings and foregoing description, the same is to be considered asillustrative and not restrictive in character—it being understood thatonly preferred embodiments have been shown and described, and that allchanges and modifications that come within the spirit of the inventionare desired to be protected. Undoubtedly, many other “variations” on the“themes” set forth hereinabove will occur to one having ordinary skillin the art to which the present invention most nearly pertains, and suchvariations are intended to be within the scope of the invention, asdisclosed herein.

For example, the resulting spring contact elements may be heat-treatedto enhance their mechanical characteristics, either while they areresident upon the sacrificial substrate or after they are mounted toanother substrate or an electronic component. Also, any heat incident tomounting (e.g., by brazing) the spring contact elements to a componentcan advantageously be employed to “heat treat” the material of thespring contact element.

For example, a comparable spring contact element could be fabricatedwithout etching into the sacrificial substrate, by disposing multiplelayers of photoresist (masking material) onto a substrate, formingopenings therein, seeding the opening for electroplating or the like,building up a metallic mass within the opening, and removing thephotoresist. Such a technique would be particularly well suited tofabricating spring contact elements directly upon active semiconductordevices.

For example, it is within the scope of this invention that the contactstructure can be fabricated on or attached to active semiconductordevices.

1. A microelectronic spring contact element, comprising: an elongatemember having a base portion, a contact portion opposite the baseportion, and a central body portion connected at one end to the baseportion and at an opposite end to the contact potion, wherein a width ofthe central body portion in a first plane tapers from the one end to theopposite end and a thickness of the central body portion in a secondplane perpendicular to the first plane tapers from the one end to theopposite end; an end of the contact portion is offset in a firstdirection from the central portion by a non-zero distance “d1”; an endof the base portion is offset in a second direction opposite the firstdirection from the central portion by a non-zero distance “d2”; wherein:the end of the base portion is adapted in use to be mounted to a firstelectronic component; and the end of the contact portion is adapted inuse to make a pressure connection with a second electronic component,wherein the end of the base portion and the end of the contact portionare substantially parallel to the central body portion.
 2. Themicroelectronic spring contact element of claim 1, wherein the contactportion comprises a contact tip structure extending from the end of thecontact portion.
 3. The microelectronic spring contact element of claim2, wherein the contact tip structure comprises a pyramid shape or atruncated pyramid shape.
 4. The microelectronic spring contact elementof claim 1, wherein the contact tip structure is attached to the end ofthe contact portion.
 5. The microelectronic spring contact element ofclaim 1, wherein the contact structure is integrally formed with thecontact portion.
 6. The microelectronic spring contact element of claim1, wherein a width in the first plane of the end of the base portion isgreater than a width in the first plane of the end of the contactportion.
 7. The microelectronic spring contact element of claim 6,wherein a thickness in the second plane of the end of the base portionis greater than a thickness in the second plane of the end of thecontact portion.
 8. The microelectronic spring contact element of claim1, wherein a thickness in the second plane of the end of the baseportion is greater than a thickness in the second plane of the end ofthe contact portion.
 9. The microelectronic spring contact element ofclaim 1, wherein the thickness of the central body portion tapers fromthe one end to the opposite end at a taper angle of between 2-6 degrees.10. The microelectronic spring contact element of claim 9, wherein thewidth of the central body portion tapers from the one end to theopposite end at a taper angle of between 2-6 degrees.
 11. Themicroelectronic spring contact element of claim 1, wherein the width ofthe central body portion tapers from the one end to the opposite end ata taper angle of between 2-6 degrees.
 12. The microelectronic springcontact element of claim 1, wherein a length parallel to the first planeof the elongate member from the base portion to the contact portion isgreater than a height parallel to the second plane of the elongatemember from the end of the base portion to the end of the contactportion.
 13. The microelectronic spring contact element of claim 12, thelength is at least five times the height.
 14. The microelectronic springcontact element of claim 13, wherein the length is in a range of 40-500mils.
 15. The microelectronic spring contact element of claim 13,wherein the length is in a range of 60-100 mils.
 16. The microelectronicspring contact element of claim 12, wherein the length is in a range of40-500 mils.
 17. The microelectronic spring contact element of claim 12,wherein the length is in a range of 60-100 mils.